1. Field of the Invention
The present invention relates to a monitoring apparatus for plasma process, which detects the change of conditions of a plasma processing apparatus in order to decrease the defective products due to the change of the apparatus conditions and to select the products which may be defective.
2. Prior Art
Recently, in the manufacture of semiconductor, magnetic storage media, optical storage media, liquid crystal display units and others, to form various kinds of thin films on a substrate, an apparatus which can accurately control the thickness of film is required. To satisfy this condition, plasma processing apparatus which employs plasma technologies have been utilized.
This plasma processing apparatus is shown in FIG. 1. As shown in FIG. 1, The plasma processing apparatus comprises a film forming unit 10 for forming a thin film, a power supply 20 for supplying high voltage to the film forming unit 10, a vacuum pump 30 for forming the forming unit 10 into a vacuum and a gas tank 40 for supplying sputtering gas to the film forming unit 10.
The film forming unit 10 is a sputtering apparatus for forming the thin film by generating plasma with glow discharge. The film forming unit 10 comprises a cathode 50 to be a target and a substrate holder 60, which are faced to the other, and a substrate 70 on which a thin film is formed is mounted on the substrate holder 60.
The film forming unit 10 is formed a vacuum of 10.sup.-2 -10.sup.-4 Torr by the vacuum pump 30, and the sputtering gas such as argon is supplied to the unit 10 from the gas tank 40. Next, the voltage of -500 V is applied to the cathode 50 by the power supply 20 through a connecting cable 80, and then, the glow discharge is generated.
Ions generated by the glow discharge collide to the cathode 50 and then neutral particles that are substance of the cathode 50 and secondary electrons are emitted. The emitted neutral particles are deposited to the substrate 70 to form a thin film 70a.
However, in the above-described plasma processing apparatus, the abnormal discharge such as arc discharge is generated due to the fluctuation of the power supply 20, the consumption of the cathode 50, the fluctuation of the vacuum, and the change of the components and density of the sputtering gas. In a case that the abnormal discharge is generated, the thin film may partially have the different properties, which is a problem in the thin film forming process.
In order to decrease the generation of the different properties in the thin film, the skilled operator monitors and controls the film forming unit 10, the power supply 20, the vacuum pump 30, the gas tank 40 and others, and after the process, all products are inspected to separate the defective products.
Further, the quality of thin film depends on the materials and the apparatus and the peripheral devices in the film forming process. Keeping the reliance and uniformity of the plasma generating mechanism is difficult since checking the every parameters is hard and keeping the normal conditions of the film forming process in long time is difficult.
In particular, generating the plasma stably and keeping the stable condition are very difficult.